Mutagenicity in surface waters: new insights into an old problem

Discharge of treated wastewater from Bitterfeld-Wolfen to the River Mulde. Image: SOLUTIONS

A guest post by Werner Brack of the SOLUTIONS project

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Mutagenicity – where chemicals interact with our genes, resulting in harmful mutations, potentially causing cancer and damaging our offspring – is a major environmental concern. Mutagenicity in drinking water resources – including many European rivers, lakes and reservoirs – is a particular problem. Although rarely investigated, similar mutation effects can be observed in wildlife, and it is still under debate whether mutagens can damage whole populations.

Mutagenic effects can be detected in water and other samples using biotests such as the Ames test, which uses different strains of Salmonella bacteria. In the River Rhine and other rivers and lakes mutagenicity has been frequently detected, however there has been no success in identifying the compounds causing this effect.

New research by the SOLUTIONS project is providing new insights into these problems. Investigations on the River Rhine and the Rivers Mulde and Holtemme from the Elbe catchment provide evidence on possible drivers of mutagenicity and of its effects on wild populations of freshwater shrimps (Gammarus pulex).

The River Mulde is impacted by historical pressures from Bitterfeld-Wolfen, one of the oldest chemical industrial sites in Germany, which still supports multiple chemical production processes today. Wastewater is discharged after treatment in a large mixed industrial and municipal treatment plant to the river.

Two years ago, scientists from the Helmholtz Centre for Environmental Research found mutagenic effects downstream from the wastewater discharge (Hug et al., 2015). Now they are able to identify causes. Two potent mutagenic aromatic amines (2,3- and 2,8-phenazindiamine) were emitted into the river; compounds that probably stem from dye production, and explain up to 80 % of the observed mutagenic effects (Muz et al., 2017a) In short, chemical pollution on the river is causing mutations in aquatic organisms, causing significant stress to the ecosystem health and status.

In the River Rhine the situation is more complex. As there are multiple water inputs from tributaries and treated wastewater from industries and households, it is not one or a couple of chemicals causing mutagenicity: instead a mixture effect. However, the latest investigations show that it is not just the poorly-defined and complex mixture of ten thousands of chemicals and effects adding up (Muz et al., 2017b). There are clear drivers of mixture mutagenicity. Aromatic amines from industry meet carboline alkaloids such as norharman known from coffee, tobacco smoke and well-cooked food.

Interestingly, these drivers are not (or only very weakly) mutagenic as individual compounds. However, when taken up by organism together as a mixture they react to highly potent mutagens. Although this effect explained only a part of the found mutagenicity in the Rhine River it may provide a key for better understanding environmental mutagenicity.

Diagram of mixture mutagenicity found in River Rhine. Reproduced from Muz et al. 2017

And what about new indications that mutagenicity is affecting wildlife populations? To demonstrate these effects SOLUTIONS scientists investigated another water body, the River Holtemme in Saxony-Anhalt, Germany. There are indications that mutagenic wastewater components may impact on the genetic diversity of freshwater shrimps. Downstream of a wastewater effluent discharge which caused mutagenic effects in the Ames test, genetic diversity of freshwater shrimps dropped. At the same time, so-called private alleles were occurring, exotic pieces of DNA that are an indication of mutations.

The evidence is increasingly clear: chemical pollution can cause mutations to aquatic organisms which damage their health and diversity. The question, then, is how to find policy and management solutions to limit chemical pollution wherever possible.

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